Consumers are very concerned about safety of electronic products using laser light because a few milliwatts (mW) of laser irradiation would suffice to cause harm to the eyes. Therefore, the use of laser light must satisfy safety classification as:
Class I/1: the laser light in the device, such as a CD player, is safe. This is because the laser light is contained and enclosed in the device.
Class II/2: the laser light used under normal circumstances is safe, and the blink reflex of human eyes can avoid human eyes being harmed. The laser power of such device, such as a laser pointer, is normally lower than 1 mW.
Class IIIa/3R: the laser power normally would reach 5 mW, and there is a little risk that the laser light may cause harm to the eyes even in a split of the time as short as the blink reflex of the eyes. Watching such light beam for a few seconds may cause harm to the retina.
Class IIIb/3B: the eyes will be harmed immediately when exposed to the laser light.
Class IV/4: the laser light will singe the skin, and under some circumstances, even scattered laser light may cause harm to the eyes and the skin.
The laser projection system, having small size, high contrast, wide gamut and focus free, has been widely used and has gained greater and greater popularity. However, if the laser light is used in a projection device, the above safety classification must be satisfied.
To avoid the laser light causing harm to the eyes, an image sensor is disposed on the laser projection system. The image sensor detects the projection range, and sends the detection results back to the laser projection system to determine whether someone appears within the projection range and the position of this person. Normally, such laser projection system requires complicated algorithms and high circuit costs.
Another way of laser safety protection can be achieved by disposing a photo-intensity sensor on the laser projection system to detect the intensity of reflective light within the projection range. If it is detected that an object is moving within the projection range, either the power of the laser light source is reduced or the laser light source is turned off.
The photo-intensity sensor is classified into an active far-infrared light intensity sensor and a passive far-infrared light intensity sensor. The passive far-infrared light intensity sensor detects whether there are charges generated according to temperature changes. However, if someone is already within the projection range before the laser projection device is booted, then the passive far-infrared light intensity sensor would not be able to detect this person.
The active far-infrared light intensity sensor emits an infrared light beam to detect the movement of an object. The active far-infrared light intensity sensor determines whether there are any objects moving according to whether the reflective light intensity varies with the time. Therefore, the active far-infrared light intensity sensor cannot detect the static object.